The present invention relates to a power source for an electric discharge machine such as a die sinking type electric discharge machine or a wire type electric discharge machine for machining a metal or the like by using discharge energy from a capacitor.
A conventional power source circuit for an electric discharge machining power source for performing machining by discharge of the capacitor, is illustrated in FIG. 1. Referring to FIG. 1, reference symbol E denotes a power source; R1, a current limiting resistor; C1, a charging/discharging capacitor; P, an electrode; W, a workpiece; Q1, a transistor as a switching element for charging the capacitor C1; G1, a base of the transistor Q1; Q2, a transistor as a switching element for discharging the capacitor C1; and G2, a base of the transistor Q2. Reference symbols L1 and L2 respectively denote stray inductances present in the power source circuit. In the circuit having the arrangement described above, a pulse is supplied to the base G1 of the transistor Q1 which is then turned on, so that the capacitor C1 is charged. Then, the transistor Q2 is turned on after the transistor Q1 is turned off, and a voltage charged by the capacitor C1 is applied between the electrode P and the workpiece W. A discharge current from the capacitor C1 flows as a discharge spark between the electrode P and the workpiece W, thereby performing electric discharge machining. When a resistance of the current limiting resistor R1 is decreased to charge the capacitor C1 at a high speed, the resistor R1 generates heat, result in large energy loss. Further, when the transistor Q1 is turned off, energy stored by the stray inductance L1 in the power source circuit is applied as a large surge voltage in an emitter-collector path of the transistor Q1 to damage the transistor Q1, resulting in inconvenience. As a result, the current cannot be increased and high-speed charging of the capacitor C1 cannot be performed.